The present invention relates generally to planar sensors. More particularly, the present invention relates to a method of supporting and holding a planar sensing element of an exhaust constituent sensor in a robust simple package.
Exhaust constituent sensors have been used for many years in automotive vehicles to sense the presence of constituents in exhaust gasses (e.g., oxygen, hydrocarbons, nitrous oxides) and to sense, for example, when an exhaust gas content switches from rich to lean or lean to rich. One known type of exhaust constituent sensor includes a flat plate exhaust sensor formed of various layers of ceramic and electrolyte materials laminated and sintered together with electrical connections placed between the layers in a known manner.
Because automotive exhaust constituent sensors are mounted to members of the vehicle exhaust flow system, the sensors must be durable, able to withstand vibration and jarring such as would occur during installation and normal vehicle operation and able to withstand shock from the occasional stone or other small road debris that may happen to be thrown at the sensor, for example, by the vehicle""s tires.
Typically, great care is required when packaging and holding the flat plate sensing element within the outer housing (body) of the exhaust constituent sensor. The flat plate sensing element can be both difficult and expensive to package within the body of the exhaust constituent sensor since it generally has one dimension that is very thin and is usually made of a brittle material. For example, one method of protecting the planar sensing element is to encase and hold the planar sensing element in proper position within a glass tube which is itself bonded to a metal shield of the exhaust constituent sensor. This process is time consuming and is therefore expensive in terms of manufacturing costs. Consequently, great care and time consuming effort must be taken to prevent the planar sensing element from being damaged by exhaust, heat, impact, vibration, the environment, etc.
The present invention comprises exhaust constituent sensors and a method of manufacturing same, and more particularly relates to a method of supporting and holding a planar sensing element in a robust simple package. One embodiment comprises an exhaust constituent sensor, comprising a planar sensing element securely held in place within a tubular shield by disposing a high temperature mat support between the tubular shield and the planar sensing element. It being understood that the high temperature mat support of the present invention comprises mat materials which are designed to withstand the heat generated in a spark ignition environment.
The high temperature mat support positions and secures the planar sensing element within the tubular shield and also advantageously provides an exhaust gas barrier in the sensor so that exhaust gas is blocked from a central portion and an upper portion of the planar sensing element. The high temperature mat support filter provides an instrument to dissipate heat from the inside of the sensor. The dissipation of heat from the planar sensing element reduces the possibility that excessive heat contacts the electrical connection of the planar sensing element during operation.
Advantageously, this invention provides an exhaust constituent sensor having improved holding of the planar sensing element within a sensor housing which provides improved resistance to failures caused by exposures to exhaust, heat, impact, vibration, and other environmental hazards which adversely effect the performance of the exhaust constituent sensor. Furthermore, the sensor of the present invention greatly simplifies the overall process of packaging a planar sensing element within an exhaust constituent sensor and as a result reduces the associated costs of the process.